1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a slot motor assembly for enabling an electromagnetic blow-open operation to be generated.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. 5,910,760 issued Jun. 8, 1999 to Malingowski, et al, each of which is assigned to the assignee of the present application and incorporated herein by reference.
It is known to implement an arc extinguisher assembly within a circuit breaker, the function of which is to receive and dissipate electrical arcs that are created upon separation of the breaker's contacts. Commonly, such an arc extinguisher assembly includes an arc chute within which are positioned spaced-apart arc chute plates.
It is also known to implement a slot motor assembly within a circuit breaker in order to provide a faster separation of its contacts than can normally occur as the result of a typical tripping operation. The current flowing between the contacts induces a magnetic field into a closed magnetic loop provided by magnetic plates of the slot motor assembly. This magnetic field electro-magnetically interacts with the current in such a manner as to have a tendency to move the moveable contact arm in the opening direction. The higher the magnitude of the current, the stronger the magnetic interaction. For very high current (an overcurrent condition), the above process provides a blow-open operation in which the moveable contact arm independently and forcefully rotates upwardly and separates the contacts.
The housing of the slot motor assembly is typically molded, and may be formed of a material that evolves gas upon interaction with an electrical arc. The evolved gas helps move the arc toward the arc chute and flatten it against the arc chute plates in the form of a band or ribbon. This shape makes it easier to split the arc and move it into the arc chute where it is dissipated.
Unfortunately, the housing of the slot motor assembly sometimes is thinned and can become porous due to the ablating of the gas-evolving material during arcing events. In the prior art, the potential thinned and porous areas of the housing can allow ionized gas or the arc itself to pass through to the magnetic plates which, undesirably, can create an electrical short. In addition, gas-evolving materials used for the housing typically have less-than-desirable molding properties, such as brittleness and high warpage, which make it difficult to mold the housing into a form providing sufficient protection to the magnetic plates.
It would be advantageous if a circuit breaker existed having a slot motor assembly that was cost-effective and easily manufactured and that prevented ionized gas from passing through potential thinned or porous areas of the assembly's housing. It would also be advantageous if a circuit breaker existed having a slot motor assembly that enabled a more easily molded assembly housing to be implemented.